Studies testing the effects of pharmacological agents administered intracranially and systemically to squirrel monkeys will be performed to assess the role of the nucleus accumbens in motor activity. Reversible, functional lesions can be produced by the introduction of minute drug doses infused through bilaterally placed, chronically implanted cannulae. Two behavioral tests are designed to correlate motor activity with the pharmacological manipulation of dopaminergic activity. The first will screen for drug-induced, general locomotor effects by a photoelectric measure of activity per unit time. The second will test for discrete, drug-induced, temporal effects by using a reaction time paradigm. Also, portions of sessions will be filmed and taped to document descriptive observations. The primary objective is to determine the function of the nucleus accumbens in motor activity using primates so that the precursors of natural and anomalous motor conditions can be better explained.